Light-irradiation type thermal processing method and thermal processing apparatus

ABSTRACT

From a stage of preheating by a halogen lamp to irradiation with a flash by a flash lamp, a radiation thermometer is used for measuring the temperature of a back surface of a semiconductor wafer. A increased temperature ΔT is determined by which the back surface of the semiconductor wafer is increased in temperature from the preheating temperature by irradiation with a flash. The specific heat of the semiconductor wafer has a known value. Further, the increased temperature ΔT is proportionate to the magnitude of energy applied to a front surface of the semiconductor wafer by irradiation with a flash. Thus, a front surface attained temperature of the semiconductor wafer can be determined using the increased temperature ΔT of the back surface of the semiconductor wafer during irradiation with a flash.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a divisional of U.S. patentapplication Ser. No. 15/205,386, filed Jul. 8, 2016, by Takayuki AOYAMA,entitled “LIGHT-IRRADIATION TYPE THERMAL PROCESSING METHOD AND THERMALPROCESSING APPARATUS,” which claims priority to Japanese PatentApplication No. 2015-160420, filed Aug. 17, 2015. The entire contents ofeach of these patent applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a thermal processing method and athermal processing apparatus for heating a precision electronicsubstrate (hereinafter simply called a “substrate”) in the form of athin plate such as a semiconductor wafer by irradiating the substratewith a flash.

Description of the Background Art

Impurity introduction performed to form a pn junction in a semiconductorwafer is an essential step in manufacturing process of a semiconductordevice. At present, impurities are introduced generally by ionimplantation process and subsequent annealing process. The ionimplantation process is a technique of implanting impurities physicallyby ionizing an impurity element such as boron (B), arsenic (As), orphosphorous (P), and making the impurity ions collide with thesemiconductor wafer at a highly accelerated voltage. The implantedimpurities are activated by the annealing process. If the annealingtakes about several seconds or more, the implanted impurities arediffused deeply by heat and a resultant junction reaches a depth greaterthan is necessary. This might become an obstacle to favorable formationof a device.

Flash lamp annealing (FLA) has attracted attention in recent years as anannealing technique of heating a semiconductor wafer in an extremelyshort period of time. The flash lamp annealing is a thermal processingtechnique of increasing the temperature only of a front surface withimplanted impurities of a semiconductor wafer in an extremely shortperiod of time (several milliseconds or less) by irradiating the frontsurface of the semiconductor wafer with a flash using a xenon flash lamp(in the below, a lamp simply called a “flash lamp” means a xenon flashlamp).

The spectral distribution of light emitted from a xenon flash lampranges from an ultraviolet region to a near-infrared region, has ashorter wavelength than light from a conventional halogen lamp, andsubstantially agrees with a base absorption band of a siliconsemiconductor wafer. Thus, irradiating the semiconductor wafer with aflash from the xenon flash lamp does not produce much transmitted light,so that the temperature of the semiconductor wafer can be increasedrapidly. Additionally, it has become known that irradiation with a flashin an extremely short period of time of several milliseconds or less canincrease the temperature only of a front surface and its vicinity of thesemiconductor wafer selectively. As a result, increasing a temperaturein an extremely short period of time by the xenon flash lamp can realizeonly activation of impurities without causing deep diffusion of theimpurities.

During thermal process not limited to flash heating, what is importantis to control the temperature of a semiconductor wafer properly. Forsuch control, the temperature of the semiconductor wafer being processedthermally should be measured accurately. During thermal process on thesemiconductor wafer, a temperature is typically measured using anon-contact radiation thermometer. For accurate temperature measurementwith the radiation thermometer, the emissivity of a measurement targetshould be known. Meanwhile, the emissivity of the semiconductor wafer isknown to differ largely in a manner that depends on a pattern or a filmformed on its front surface. Unless the emissivity is established,temperature measurement with the radiation thermometer is impossible.

According to the suggestion of US 2012/0288970, after the temperature ofa front surface and that of a back surface of a semiconductor waferbecome equal to each other during irradiation with a flash, theemissivity of the front surface of the wafer is determined based on thetemperature of the wafer measured with a radiation thermometer on a sidecloser to the back surface and light intensity measured on a side closerto the front surface. Then, by using the determined emissivity, thetemperature of the front surface of the semiconductor wafer during theirradiation with a flash is determined.

However, according to the technique disclosed in US 2012/0288970, asensor should be provided for each of the side closer to the frontsurface and the side closer to the back surface of the semiconductorwafer for measurement. This results in a complicated mechanism and acomplicated algorithm for the determination. Additionally, while avariety of materials have been used for semiconductor purposes in recentyears, there has been a strong demand for measuring the temperature of afront surface of a substrate easily where emissivity is very difficultto measure such as a substrate including a silicon base and an epitaxialfilm of germanium formed on the base, for example.

SUMMARY OF THE INVENTION

The present invention is intended for a thermal processing method forheating a substrate by irradiating the substrate with a flash.

According to one aspect of this invention, the thermal processing methodcomprises the steps of: (a) preheating the substrate by increasing thesubstrate in temperature to a predetermined preheating temperaturebefore irradiating the substrate with a flash; (b) heating the substrateincreased in temperature to the preheating temperature by irradiating afront surface of the substrate with a flash; (c) measuring an increasedtemperature by which a back surface of the substrate is increased intemperature from the preheating temperature by irradiation with a flash;and (d) determining a front surface attained temperature of thesubstrate during irradiation with a flash based on the increasedtemperature.

The front surface attained temperature of the substrate can bedetermined only by measuring the temperature of the back surface of thesubstrate. Thus, the temperature of the front surface of the substratecan be measured with a simple structure irrespective of the condition ofthe front surface of the substrate.

Preferably, in the step (d), the front surface attained temperature isdetermined using an integral of the increased temperature.

Measurement accuracy can be increased.

The present invention is also intended for a thermal processingapparatus for heating a substrate by irradiating the substrate with aflash.

According to one aspect of this invention, the thermal processingapparatus comprises: a chamber that houses the substrate; a holdingmember to hold the substrate inside the chamber; a flash lamp thatirradiates a front surface of the substrate held by the holding memberwith a flash; a preheating part that increases the substrate intemperature to a predetermined preheating temperature before thesubstrate is irradiated with a flash from the flash lamp; a back surfacetemperature measuring part that measures the temperature of a backsurface of the substrate held by the holding member; and a front surfacetemperature determining part that determines a front surface attainedtemperature of the substrate during irradiation with a flash based on anincreased temperature measured by the back surface temperature measuringpart by which the back surface of the substrate is increased intemperature from the preheating temperature by irradiation with a flash.

The front surface attained temperature of the substrate can bedetermined only by measuring the temperature of the back surface of thesubstrate. Thus, the temperature of the front surface of the substratecan be measured with a simple structure irrespective of the condition ofthe front surface of the substrate.

Preferably, the front surface temperature determining part determinesthe front surface attained temperature using an integral of theincreased temperature.

Measurement accuracy can be increased.

It is therefore an object of the present invention to measure thetemperature of a front surface of a substrate with a simple structureirrespective of the condition of the front surface of the substrate.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view showing the structure of a thermalprocessing apparatus according to the present invention;

FIG. 2 is a perspective view showing an entire appearance of a holdingmember;

FIG. 3 is a plan view of the holding member as viewed from the uppersurface thereof;

FIG. 4 is a side view of the holding member as viewed from a lateralside thereof;

FIG. 5 is a plan view of a transfer mechanism;

FIG. 6 is a side view of the transfer mechanism;

FIG. 7 is a plan view showing arrangement of a plurality of halogenlamps;

FIG. 8 is a block diagram showing the structure of a controller;

FIG. 9 schematically shows change in the temperature of a semiconductorwafer measured with a radiation thermometer; and

FIG. 10 shows a correlation between an increased temperature of a backsurface of a semiconductor wafer and an attained temperature of a frontsurface of the semiconductor wafer during irradiation with a flash.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention is described in detailbelow by referring to the drawings.

FIG. 1 is a vertical sectional view showing the structure of a thermalprocessing apparatus 1 according to the present invention. The thermalprocessing apparatus 1 of this preferred embodiment is a flash lampannealing apparatus that heats a semiconductor wafer W of a circularplate shape as a substrate by irradiating the semiconductor wafer W witha flash. Although not specifically limited, the size of a semiconductorwafer W to be processed is 300 mm or 450 mm in diameter, for example. Asemiconductor wafer W before being transported into the thermalprocessing apparatus 1 contains implanted impurities. The implantedimpurities are activated by thermal process in the thermal processingapparatus 1. In order to facilitate understanding, in FIG. 1 and itssubsequent figures, the dimensions of components and the numbers of thecomponents are exaggerated or simplified, where necessary.

The thermal processing apparatus 1 includes a chamber 6 that houses asemiconductor wafer W, a flash heating unit 5 with a plurality ofbuilt-in flash lamps FL, and a halogen heating unit 4 with a pluralityof built-in halogen lamps HL. The flash heating unit 5 and the halogenheating unit 4 are arranged above and below the chamber 6 respectively.The thermal processing apparatus 1 further includes a holding member 7and a transfer mechanism 10 provided inside the chamber 6. The holdingmember 7 holds a semiconductor wafer W in a horizontal posture. Thetransfer mechanism 10 transfers a semiconductor wafer W between theholding member 7 and a place outside the apparatus. The thermalprocessing apparatus 1 further includes a controller 3 that controlseach operating mechanism of the halogen heating unit 4, the flashheating unit 5, and the chamber 6 to realize thermal process on asemiconductor wafer W.

The chamber 6 is formed of chamber windows made of quartz attached to anupper part and a lower part of a columnar chamber side section 61. Thechamber side section 61 has a substantially columnar shape with an upperopening and a lower opening. An upper chamber window 63 is attached tothe upper opening to close the upper opening. A lower chamber window 64is attached to the lower opening to close the lower opening. The upperchamber window 63 forming a ceiling part of the chamber 6 is a circularplate member made of quartz. The upper chamber window 63 functions as aquarts window to cause flashes emitted from the flash heating unit 5 toreach the inside of the chamber 6. The lower chamber window 64 forming afloor part of the chamber 6 is also a circular plate member made ofquarts. The lower chamber window 64 functions as a quarts window tocause light emitted from the halogen heating unit 4 to reach the insideof the chamber 6.

A reflection ring 68 and a reflection ring 69 are attached to an upperpart and a lower part respectively of an inner wall surface of thechamber side section 61. The reflection rings 68 and 69 are both formedinto an annular shape. The upper reflection ring 68 is attached by beingfitted from above the chamber side section 61. The lower reflection ring69 is attached by being fitted from below the chamber side section 61and then fastened with a screw not shown in the drawings. Specifically,the reflection rings 68 and 69 are attached to the chamber side section61 in a manner that allows the reflection rings 68 and 69 to be removedfreely from the chamber side section 61. Space inside the chamber 6,specifically, space surrounded by the upper chamber window 63, the lowerchamber window 64, the chamber side section 61, and the reflection rings68 and 69 is defined as thermal processing space 65.

Attaching the reflection rings 68 and 69 to the chamber side section 61forms a recessed part 62 in the inner wall surface of the chamber 6. Therecessed part 62 is surrounded by a central area of the inner wallsurface of the chamber side section 61 not covered by the reflectionrings 68 and 69, a lower end surface of the reflection ring 68, and anupper end surface of the reflection ring 69. The recessed part 62 isformed into an annular pattern along the inner wall surface of thechamber 6 in the horizontal direction. The recessed part 62 surroundsthe holding member 7 to hold a semiconductor wafer W.

The chamber side section 61 and the reflection rings 68 and 69 are madeof a metallic material having excellent strength and resistance to heat(such as stainless steel). The inner circumferential surfaces of thereflection rings 68 and 69 are mirror surfaces plated with electrolyticnickel.

A transport opening section (furnace opening) 66 is provided in thechamber side section 61 through which a semiconductor wafer W istransported into and out of the chamber 6. The transport opening section66 can be opened and closed by a gate valve 185. The transport openingsection 66 is communicatively connected to the outer peripheral surfaceof the recessed part 62. Thus, while the gate valve 185 opens thetransport opening section 66, a semiconductor wafer W can be transportedinto and out of the thermal processing space 65 through the transportopening section 66 and the recessed part 62. If the gate valve 185closes the transport opening section 66, the thermal processing space 65inside the chamber 6 becomes hermetically sealed space.

A gas supply hole 81 is formed in an upper part of the inner wall of thechamber 6 through which processing gas (in this preferred embodiment,nitrogen gas (N₂)) is supplied into the thermal processing space 65. Thegas supply hole 81 is formed above the recessed part 62 and may beformed in the reflection ring 68. The gas supply hole 81 iscommunicatively connected to a gas supply pipe 83 through buffer space82 formed into an annular shape inside the side wall of the chamber 6.The gas supply pipe 83 is connected to a nitrogen gas source 85. A valve84 is interposed in a pathway of the gas supply pipe 83. Opening thevalve 84 supplies nitrogen gas from the nitrogen gas source 85 into thebuffer space 82. The nitrogen gas having flown into the buffer space 82spreads through the buffer space 82 lower in fluid resistance than thegas supply hole 81 and is then supplied into the thermal processingspace 65 through the gas supply hole 81. The processing gas is notlimited to nitrogen gas but it may also be an inert gas such as argon(Ar) or helium (He), or may be a reactive gas such as oxygen (O₂),hydrogen (H₂), chlorine (Cl₂), hydrogen chloride (HCl), ozone (O₃), orammonia (NH₃).

A gas exhaust hole 86 is formed in a lower part of the inner wall of thechamber 6 through which gas is exhausted from the thermal processingspace 65. The gas exhaust hole 86 is formed below the recessed part 62and may be formed in the reflection ring 69. The gas exhaust hole 86 iscommunicatively connected to a gas exhaust pipe 88 through buffer space87 formed into an annular shape inside the side wall of the chamber 6.The gas exhaust pipe 88 is connected to an exhaust unit 190. A valve 89is interposed in a pathway of the gas exhaust pipe 88. Opening the valve89 exhausts gas from the thermal processing space 65 and discharges thegas into the gas exhaust pipe 88 through the gas exhaust hole 86 and thebuffer space 87. The gas supply hole 81 and the gas exhaust hole 86 mayeach be formed in multiple places in the peripheral direction of thechamber 6, or they may be formed as slits. The nitrogen gas source 85and the exhaust unit 190 may be mechanisms provided in the thermalprocessing apparatus 1, or may be utilities of a factory where thethermal processing apparatus 1 is placed.

A gas exhaust pipe 191 is connected to the tip of the transport openingsection 66 through which gas is further exhausted from the thermalprocessing space 65. The gas exhaust pipe 191 is connected through avalve 192 to the exhaust unit 190. Opening the valve 192 exhausts gasfrom the inside of the chamber 6 through the transport opening section66.

FIG. 2 is a perspective view showing an entire appearance of the holdingmember 7. FIG. 3 is a plan view of the holding member 7 as viewed fromthe upper surface thereof. FIG. 4 is a side view of the holding member 7as viewed from a lateral side thereof. The holding member 7 includes abase ring 71, coupling sections 72, and a susceptor 74. The base ring71, the coupling sections 72, and the susceptor 74 are all made ofquartz. Specifically, the entire holding member 7 is entirely made ofquartz.

The base ring 71 is an annular quartz member. The base ring 71 issupported on the wall surface of the chamber 6 by being placed on thebottom surface of the recessed part 62 (see FIG. 1). Multiple couplingsections 72 (in this preferred embodiment, four coupling sections 72)are provided in upright positions on the upper surface of the annularbase ring 71 to be arranged along the circumferential direction of thebase ring 71. The coupling sections 72 are also quartz members and arefixedly attached by welding to the base ring 71. The base ring 71 mayalso be formed into a circular arc defined by forming a cut in part ofan annular shape.

The susceptor 74 in the form of a flat plate is supported by the fourcoupling sections 72 on the base ring 71. The susceptor 74 is a flatplate member of a substantially circular shape made of quarts. Thesusceptor 74 is larger in diameter than a semiconductor wafer W.Specifically, the size of the susceptor 74 in a plane is larger thanthat of a semiconductor wafer W. Multiple guide pins 76 (in thispreferred embodiment, five guide pins 76) are provided in uprightpositions on the upper surface of the susceptor 74. The five guide pins76 are provided along the circumference of a circle concentric with theouter circumferential circle of the susceptor 74. The diameter of thecircle along which the five guide pins 76 are arranged is slightlylarger than the diameter of a semiconductor wafer W. All the guide pins76 are also made of quartz. The guide pins 76 may be processed from aningot of quartz to be integral with the susceptor 74. Alternatively, theguide pins 76 may be processed separately from the susceptor 74 andattached to the susceptor 74 by welding, for example.

The four coupling sections 72 provided in upright positions on the basering 71 and the lower surface of a peripheral area of the susceptor 74are fixedly attached by welding. Specifically, the susceptor 74 and thebase ring 71 are fixedly coupled to each other via the coupling sections72, so that the holding member 7 is an integrally formed quartz member.The base ring 71 of the holding member 7 is supported on the wallsurface of the chamber 6, thereby attaching the holding member 7 to thechamber 6. While the holding member 7 is attached to the chamber 6, thesusceptor 74 of a substantially circular plate shape is placed in ahorizontal posture (a posture that makes the normal line thereof agreewith the vertical direction). A semiconductor wafer W transported intothe chamber 6 is placed and held in a horizontal posture on thesusceptor 74 of the holding member 7 attached to the chamber 6. Asemiconductor wafer W is placed inside the circle defined by the guidepins 76 to prevent displacement in position of the semiconductor wafer Win the horizontal direction. The number of the guide pins 76 is notlimited to five, but it may be any number that can prevent displacementin position of a semiconductor wafer W.

As shown in FIGS. 2 and 3, an opening area 78 and a cut 77 are formed inthe susceptor 74 to penetrate through the susceptor 74 vertically. Thecut 77 is provided to let a probe tip of a thermocouple contactthermometer 130 pass therethrough. The opening area 78 is provided tomake a radiation thermometer 120 receive light (infrared light) emittedfrom the lower surface of a semiconductor wafer W held on the susceptor74. The radiation thermometer 120 and the contact thermometer 130 areboth provided on a side closer to a back surface of a semiconductorwafer W held on the holding member 7. The radiation thermometer 120 isformed by using a pyrometer, for example. The radiation thermometer 120receives light emitted from a back surface of a semiconductor wafer Wheld on the holding member 7 to measure the temperature of the backsurface. Four through holes 79 are further formed in the susceptor 74.The through holes 79 penetrate through the susceptor 74 for transfer ofa semiconductor wafer W with lift pins 12 of the transfer mechanism 10described later.

FIG. 5 is a plan view of the transfer mechanism 10. FIG. 6 is a sideview of the transfer mechanism 10. The transfer mechanism 10 includestwo transfer arms 11. The transfer arms 11 are formed into a circulararc conforming to the substantially annular shape of the recessed part62. Two lift pins 12 are provided in upright positions on each of thetransfer arms 11. Each of the transfer arms 11 can be caused to pivot bya horizontal movement mechanism 13. The horizontal movement mechanism 13moves the transfer arms 11 in a pair horizontally between a transferoperating position (a position with solid lines of FIG. 5) where asemiconductor wafer W is transferred to and received from the holdingmember 7, and a retracted position (a position with alternate long andtwo short dashed lines of FIG. 5) where the transfer arms 11 do notoverlap a semiconductor wafer W in a plan view held on the holdingmember 7. The horizontal movement mechanism 13 may cause both thetransfer arms 11 to pivot independently by using different motors, ormay use a linking mechanism to cause the transfer arms 11 in a pair topivot in an interlocked manner by using one motor.

The transfer arms 11 in a pair are moved up and down together with thehorizontal movement mechanism 13 by an up-and-down mechanism 14. If theup-and-down mechanism 14 moves up the transfer arms 11 in a pair in thetransfer operation position, the four lift pins 12 in total pass throughthe through holes 79 (see FIGS. 2 and 3) formed in the susceptor 74 tomake the upper ends of the lift pins 12 project from the upper surfaceof the susceptor 74. If the up-and-down mechanism 14 moves down thetransfer arms 11 in a pair in the transfer operating position, the liftpins 12 are extracted from the through holes 79. Then, the horizontalmovement mechanism 13 moves the transfer arms 11 in a pair in such amanner that the transfer arms 11 are separated further from each other.In this way, each of the transfer arms 11 moves to the retractedposition. The retracted position of the transfer arms 11 in a pair isdirectly above the base ring 71 of the holding member 7. The base ring71 is placed on the bottom surface of the recessed part 62, so that theretracted position of the transfer arms 11 is defined inside therecessed part 62. An exhaust mechanism not shown in the drawings isfurther provided in a place near the driving part (horizontal movementmechanism 13 and up-and-down mechanism 14) of the transfer mechanism 10.This exhaust mechanism is configured to exhaust atmosphere around thedriving part of the transfer mechanism 10 to the outside of the chamber6.

Referring back to FIG. 1, the flash heating unit 5 arranged above thechamber 6 includes a light source formed of multiple xenon flash lampsFL (in this preferred embodiment, 30 xenon flash lamps FL), and areflector 52 provided to cover the light source from above. The lightsource and the reflector 52 are housed in a casing 51. A lamp lightradiation window 53 is attached to the bottom of the casing 51 of theflash heating unit 5. The lamp light radiation window 53 forming a floorpart of the flash heating unit 5 is a plate-like quartz window. Placingthe flash heating unit 5 above the chamber 6 makes the lamp lightradiation window 53 face the upper chamber window 63. The flash lamps FLirradiate the thermal processing space 65 with flashes traveling fromabove the chamber 6 to reach the thermal processing space 65 through thelamp light radiation window 53 and the upper chamber window 63.

The flash lamps FL are each a bar-shaped lamp of an elongatedcylindrical shape. The flash lamps FL are arranged in a plane in such amanner that the longitudinal directions thereof extend parallel to eachother along a main surface of a semiconductor wafer W held on theholding member 7 (specifically, in the horizontal direction). Thus, aplane formed by the arrangement of the flash lamps FL is a horizontalplane.

The xenon flash lamps FL each include a bar-shaped glass tube (dischargetube) filled with xenon gas inside and having opposite ends where ananode and a cathode connected to a capacitor are arranged, and a triggerelectrode provided on the outer peripheral surface of the glass tube.Xenon gas is an electrically insulating substance. Hence, even ifelectric charge is accumulated in the capacitor, electricity does notflow inside the glass tube in a normal condition. Meanwhile, if a highvoltage is applied to the trigger electrode to cause insulationbreakdown, electricity accumulated in the capacitor flows into the glasstube instantaneously to excite atoms or molecules of xenon, therebyemitting light. In these xenon flash lamps FL, electrostatic energyaccumulated in advance in the capacitors is converted to an extremelyshort light pulse from 0.1 to 100 milliseconds. Thus, the xenon flashlamps FL are characteristically capable of emitting extremely intenselight, compared to a light source such as the halogen lamps HL to belighted continuously. Specifically, the flash lamps FL are pulseemitting lamps that emit light instantaneously in an extremely shortperiod of time of less than one second. A period of time of lightemission from the flash lamps FL can be controlled using a coil constantof a lamp power source to supply power to the flash lamps FL.

The reflector 52 is provided above the flash lamps FL to cover the flashlamps FL entirely. The basic function of the reflector 52 is to reflectflashes emitted from the flash lamps FL toward the thermal processingspace 65. The reflector 52 is formed of an aluminum alloy plate and hasa surface (a surface bordering the flash lamps FL) roughened as a resultof blasting.

The halogen heating unit 4 arranged below the chamber 6 includesmultiple built-in halogen lamps HL (in this preferred embodiment, 40halogen lamps HL) housed in a casing 41 of the halogen heating unit 4.The halogen heating unit 4 is a light irradiator that uses the halogenlamps HL to irradiate the thermal processing space 65 with lighttraveling from below the chamber 6 to reach the thermal processing space65 through the lower chamber window 64, thereby heating a semiconductorwafer W.

FIG. 7 is a plan view showing arrangement of the halogen lamps HL. Theforty halogen lamps HL are arranged in two different tiers; an uppertier and a lower tier. Twenty halogen lamps HL are arranged in the uppertier closer to the holding member 7. Twenty halogen lamps HL arearranged in the lower tier farther from the holding member 7 than theupper tier. The halogen lamps HL are each a bar-shaped lamp of anelongated cylindrical shape. The 20 halogen lamps HL in each of theupper and lower tiers are arranged in such a manner that thelongitudinal directions thereof extend parallel to each other along amain surface of a semiconductor wafer W held on the holding member 7(specifically, in the horizontal direction). Thus, in each of the upperand lower tiers, a plane formed by the arrangement of the halogen lampsHL is a horizontal plane.

As shown in FIG. 7, in each of the upper and lower tiers, the halogenlamps HL are arranged more densely in a region facing a peripheral areaof a semiconductor wafer W held on the holding member 7 than in a regionfacing a central area of the semiconductor wafer W. Specifically, ineach of the upper and lower tiers, the pitch of the halogen lamps HL isshorter in a peripheral area of the lamp arrangement than in a centralarea thereof. This makes it possible to irradiate the peripheral area ofthe semiconductor wafer W with more light that is likely to causetemperature drop easily while being heated by irradiation with lightfrom the halogen heating unit 4.

A lamp group formed of the halogen lamps HL in the upper tier and a lampgroup formed of the halogen lamps HL in the lower tier are arranged tocross each other in a grid pattern. Specifically, a total of 40 halogenlamps HL are arranged in such a manner that the longitudinal directionof each halogen lamp HL in the upper tier and the longitudinal directionof each halogen lamp HL in the lower tier are orthogonal to each other.

The halogen lamps HL are each a filament type light source thatenergizes a filament in a glass tube to make the filament incandescent,thereby emitting light. The glass tube is filled with gas insidecontaining inert gas such as nitrogen or argon and a halogen element(iodine or bromine, for example) introduced in minute amount into theinert gas. Introducing the halogen element allows the temperature of thefilament to be set high while suppressing breakage of the filament.Thus, the halogen lamps HL are characteristically long lasting andcapable of emitting intense light continuously, compared to generalincandescent bulbs. Specifically, the halogen lamps HL are continuouslylighted lamps of emitting light continuously for at least one second ormore. The halogen lamps HL are long-lasting lamps for their bar shapes,and irradiate a semiconductor wafer W above the halogen lamps HL withexcellent efficiency as a result of the arrangement of the halogen lampsHL in the horizontal direction.

A reflector 43 is further provided in the casing 41 of the halogenheating unit 4 in a position below the halogen lamps HL in the two tiers(FIG. 1). The reflector 43 is to reflect light emitted from the halogenlamps HL toward the thermal processing space 65.

The controller 3 controls various operating mechanisms in the thermalprocessing apparatus 1. FIG. 8 is a block diagram showing the structureof the controller 3. The hardware structure of the controller 3 is thesame as that of a generally used computer. Specifically, the controller3 includes a CPU that is a circuit for performing various types ofcomputations, a ROM that is a read-only memory storing a basic program,a RAM that is a freely readable and writable memory storing informationof various types, and a magnetic disk 35 storing control software anddata, etc. Execution of a certain processing program by the CPU of thecontroller 3 makes process go forward in the thermal processingapparatus 1.

As shown in FIG. 8, the controller 3 includes a front surfacetemperature determining part 31 and a temperature correcting part 32.The front surface temperature determining part 31 and the temperaturecorrecting part 32 are functional processors realized by execution ofthe certain processing program by the CPU of the controller 3. Thesubstances of processes by the front surface temperature determiningpart 31 and the temperature correcting part 32 are described later.

A display part 33 is connected to the controller 3. The display part 33is, for example, a display panel such as a liquid crystal displayprovided on an outer wall of the thermal processing apparatus 1. A touchpanel may be employed as the display part 33.

In addition to the aforementioned structures, the thermal processingapparatus 1 includes various cooling structures intended to preventexcessive temperature increase of the halogen heating unit 4, the flashheating unit 5, and the chamber 6 to be caused by heat energy generatedfrom the halogen lamps HL and the flash lamps FL during thermal processon a semiconductor wafer W. For example, the wall of the chamber 6 isprovided with a water-cooled tube (not shown in the drawings). Thehalogen heating unit 4 and the flash heating unit 5 are each configuredas an air-cooled structure where heat is exhausted by a gas flow formedinside the structure. Further, air is supplied into a gap between theupper chamber window 63 and the lamp light radiation window 53 to coolthe flash heating unit 5 and the upper chamber window 63.

A procedure of processing a semiconductor wafer W taken by the thermalprocessing apparatus 1 is described next. The semiconductor wafer W tobe processed mentioned herein is a semiconductor substrate of silicon(Si) containing impurities (impurity ions) added by ion implantationprocess. The added impurities are activated through heating process bymeans of irradiation with a flash (annealing) performed in the thermalprocessing apparatus 1. The processing procedure descried below taken bythe thermal processing apparatus 1 proceeds while the controller 3controls each operating mechanism of the thermal processing apparatus 1.

First, the valve 84 for gas supply is opened and the valves 89 and 192for gas exhaust are opened, thereby starting supply and exhaust of gasto and from the inside of the chamber 6. Opening the valve 84 suppliesnitrogen gas from the gas supply hole 81 into the thermal processingspace 65. Opening the valve 89 exhausts gas from the inside of thechamber 6 through the gas exhaust hole 86. In this way, the nitrogen gassupplied from an upper part of the thermal processing space 65 in thechamber 6 flows downwardly and is then exhausted from a lower part ofthe thermal processing space 65.

Opening the valve 192 also exhausts gas from the inside of the chamber 6through the transport opening section 66. Further, the exhaust mechanismnot shown in the drawings exhausts atmosphere around the driving part ofthe transfer mechanism 10. During thermal process on a semiconductorwafer W in the thermal processing apparatus 1, nitrogen gas is suppliedcontinuously to the thermal processing space 65. The amount of thesupply is changed appropriately in a manner that depends on a processingstep.

Next, the gate valve 185 is opened to open the transport opening section66. Then, a transport robot outside the apparatus transports asemiconductor wafer W containing implanted ions into the thermalprocessing space 65 in the chamber 6 through the transport openingsection 66. The semiconductor wafer W transported into the thermalprocessing space 65 by the transport robot advances to a positiondirectly above the holding member 7 and stops at this position. Then,the transfer arms 11 in a pair of the transfer mechanism 10 movehorizontally from the retracted position to the transfer operatingposition and move up. As a result, the lift pins 12 pass through thethrough holes 79 to project from the upper surface of the susceptor 74.In this way, the semiconductor wafer W is received on the lift pins 12.

After the semiconductor wafer W is placed on the lift pins 12, thetransport robot goes out of the thermal processing space 65 and thetransport opening section 66 is closed using the gate valve 185. Then,the transfer arms 11 in a pair move down to transfer the semiconductorwafer W from the transfer mechanism 10 to the susceptor 74 of theholding member 7 and hold the semiconductor wafer W in a horizontalposture from below. The semiconductor wafer W is held by the holdingmember 7 while a front surface of the semiconductor wafer W providedwith a pattern and containing implanted impurities is placed as an uppersurface. The semiconductor wafer W is held inside the five guide pins 76on the upper surface of the susceptor 74. The transfer arms 11 in a pairhaving moved down to a place below the susceptor 74 are retracted by thehorizontal movement mechanism 13 to the retracted position,specifically, to a place inside the recessed part 62.

After the semiconductor wafer W is held from below in a horizontalposture by the holding member 7 made of quartz, the 40 halogen lamps HLof the halogen heating unit 4 are turned on in unison to startpreheating (assisted heating). Halogen light emitted from the halogenlamps HL passes through the lower chamber window 64 and the susceptor 74made of quarts to be emitted from a back surface of the semiconductorwafer W. The back surface of the semiconductor wafer W is a main surfaceopposite the front surface thereof. The back surface of thesemiconductor wafer W is generally not provided with a pattern. By beingirradiated with the light from the halogen lamps HL, the semiconductorwafer W is preheated to be increased in temperature. The transfer arms11 of the transfer mechanism 10 are retracted to a place inside therecessed part 62, so that the transfer arms 11 do not become an obstacleto the preheating by the halogen lamps HL.

The temperature of the semiconductor wafer W during thermal process ismeasured with the radiation thermometer 120. Specifically, the lightemitted from the back surface of the semiconductor wafer W and havingpassed through the opening area 78 of the susceptor 74 is received bythe radiation thermometer 120 to measure a wafer temperature. Theemissivity of a measurement target is necessary for temperaturemeasurement using the radiation thermometer 120. Meanwhile, the backsurface of the semiconductor wafer W is typically not provided with apattern or a film formed or deposited thereon and silicon is exposed atthe back surface of the semiconductor wafer W. Thus, the emissivity ofthe back surface of the semiconductor wafer W is known. The back surfaceof the semiconductor wafer W may be subjected to film deposition processaccording to processing purpose. In this case, a specific film isdeposited uniformly. Thus, like in the aforementioned absence of apattern or a film, the emissivity of this back surface of thesemiconductor wafer W is known. As a result, by receiving the lightemitted from the back surface of the semiconductor wafer W using theradiation thermometer 120, a temperature can be measured accurately withfavorable reproducibility.

FIG. 9 schematically shows change in the temperature of thesemiconductor wafer W measured with the radiation thermometer 120. Attime t1, the preheating by the halogen lamps HL is started to increasethe temperature of the semiconductor wafer W. In a precise sense, atemperature measured with the radiation thermometer 120 is that of theback surface of the semiconductor wafer W. Meanwhile, at the preheatingstage, a difference in temperature between the front surface and theback surface of the semiconductor wafer W is ignorable. Thus, thetemperature measured at this stage with the radiation thermometer 120can be regarded as the temperature of the entire semiconductor wafer W.The measured temperature of the semiconductor wafer W is transmitted tothe controller 3. The controller 3 controls outputs from the halogenlamps HL, while checking the temperature of the semiconductor wafer Wincreased by the irradiation with light from the halogen laps HL to seewhether this temperature has attained a preheating temperature T1.Specifically, based on a measured value obtained using the radiationthermometer 120, the controller 3 executes feedback control on outputsfrom the halogen lamps HL in such a manner that the temperature of thesemiconductor wafer W becomes equal to the preheating temperature T1.The preheating temperature T1 is set at a temperature from about 200 toabout 800° C., more preferably, from about 350 to about 600° C. (in thispreferred embodiment, 600° C.) that can prevent diffusion by heat of theimpurities added to the semiconductor wafer W. While the temperature ofthe semiconductor wafer W is relatively low, this temperature cannot bemeasurement easily with the radiation thermometer 120 in some cases.Thus, at the preheating stage, the contact thermometer 130 mayadditionally be used for the temperature measurement.

After the temperature of the semiconductor wafer W attains thepreheating temperature T1 at time t2, the controller 3 maintains thesemiconductor wafer W at the preheating temperature T1 for a while. Morespecifically, the controller 3 controls outputs from the halogen lampsHL at a time when the temperature of the semiconductor wafer W measuredwith the radiation thermometer 120 attains the preheating temperature T1to substantially maintain the temperature of the semiconductor wafer Wat the preheating temperature T1.

As a result of the aforementioned preheating by the halogen lamps HL,the semiconductor wafer W is entirely increased in temperature to thepreheating temperature T1. At the stage of the preheating by the halogenlamps HL, the temperature of the semiconductor wafer W is more likely todrop in a peripheral area than in a central area as heat escapes moreeasily in the peripheral area than in the central area. Meanwhile, thehalogen lamps HL in the halogen heating unit 4 are arranged more denselyin a region facing the peripheral area of the semiconductor wafer W thanin a region facing the central area of the semiconductor wafer W. Thus,the peripheral area of the semiconductor wafer W where heat escapes moreeasily is irradiated with more light, so that an in-plane temperaturedistribution of the semiconductor wafer W can be uniform at thepreheating stage. Additionally, the inner circumferential surface of thereflection ring 69 attached to the chamber side section 61 is a mirrorsurface. This inner circumferential surface of the reflection ring 69increases the amount of light to be reflected toward the peripheral areaof the semiconductor wafer W, making it possible to achieve a moreuniform in-plane temperature distribution of the semiconductor wafer Wat the preheating stage.

At time t3 when a predetermined period of time has elapsed after thetemperature of the semiconductor wafer W attains the preheatingtemperature T1, the front surface of the semiconductor wafer W isirradiated with flashes from the flash lamps FL. At this time, some ofthe flashes emitted from the flash lamps FL travel toward the inside ofthe chamber 6 directly, whereas the other flashes are reflected once bythe reflector 52 and then travel toward the inside of the chamber 6. Thesemiconductor wafer W is flash heated by being irradiated with theseflashes.

The flash heating is performed by irradiation with flashes (bursts oflight) from the flash lamps FL, so that the temperature of the frontsurface of the semiconductor wafer W can be increased in a short periodof time. Specifically, flashes emitted from the flash lamps FL areextremely short and intense bursts of light of extremely short lightpulses to be applied in a period of time from 0.1 to 100 millisecondsthat result from conversion from electrostatic energy accumulated inadvance in the capacitors. The temperature of the front surface of thesemiconductor wafer W flash heated by being irradiated with flashes fromthe flash lamps FL increases instantaneously as high as to a processingtemperature T2 of 1000° C. or more to activate the impurities implantedin the semiconductor wafer W. Then, the temperature of the front surfacedrops rapidly. In this way, the temperature of the front surface of thesemiconductor wafer W can be increased and reduced in an extremely shortperiod of time. This allows activation of the impurities implanted inthe semiconductor wafer W while suppressing diffusion of the impuritiesby heat. The semiconductor wafer W is preheated to the preheatingtemperature T1 by the halogen lamps HL before the semiconductor wafer Wis irradiated with flashes from the flash lamps FL. Thus, the frontsurface of the semiconductor wafer W can be increased in temperature tothe processing temperature T2 of 1000° C. or more by irradiation withflashes in an extremely short period of time. A period of time requiredfor activation of the impurities is extremely shorter than a period oftime required for diffusion of the impurities by heat. Thus, theactivation is completed even in a short period of time from about 0.1 toabout 100 milliseconds that does not cause diffusion of the impurities.

The temperature of the back surface of the semiconductor wafer W is alsomeasured with the radiation thermometer 120 during the irradiation withflashes from the flash lamps FL. The irradiation with flashes applies amassive amount of energy to the front surface of the semiconductor waferW in an extremely short period of time, so that the front surface of thesemiconductor wafer W is increased in temperature rapidly beforetemperature increase of the back surface of the semiconductor wafer Wduring the irradiation with flashes. In FIG. 9, the temperature of thefront surface of the semiconductor wafer W is indicated by dotted linesfor reference. This temperature is not an actually measured temperaturemeasured with the radiation thermometer 120. A temperature measured withthe radiation temperature 120 is the temperature of the back surface ofthe semiconductor wafer W indicated by solid lines of FIG. 9.

As shown by the dotted lines of FIG. 9, the front surface of thesemiconductor wafer W attains the processing temperature T2 of 1000° C.or more at the moment of the irradiation with flashes from the flashlamps FL at the time t3. Meanwhile, as shown by the solid lines of FIG.9, the temperature of the back surface of the semiconductor wafer Wexhibits substantially no increase from the preheating temperature T1 atthe moment of the irradiation with flashes. The temperature of the backsurface of the semiconductor wafer W is increased slightly at time t4delayed by a short period from the time t3 when the temperature of thefront surface of the semiconductor wafer W is increased by theirradiation with flashes. Specifically, there is a slight delay betweenthe time when the temperature of the front surface of the semiconductorwafer W is increased rapidly and the time when the temperature of theback surface of the semiconductor wafer W is increased thereafter. Thisis for the reason that it takes time to transfer heat from the frontsurface of the semiconductor wafer W where a temperature has beenincreased instantaneously by the irradiation with flashes in anextremely short period of time to the back surface of the semiconductorwafer W. For example, if the thickness of the semiconductor wafer W is0.775 mm, heat transfer from the front surface to the back surface takesabout 20 milliseconds.

As shown in FIG. 9, a temperature T3 attained by the back surface of thesemiconductor wafer W at the time t4 is considerably lower than theprocessing temperature T2 attained by the front surface of thesemiconductor wafer W at the moment of the irradiation with flashes.Specifically, the temperature of the back surface of the semiconductorwafer W is not increased as high as the temperature of the front surfacethereof. This means only the front surface and its vicinity of thesemiconductor wafer W is increased selectively by the flash heating,which can be used appropriately for forming a shallow junction.

The temperature T3 attained by the back surface of the semiconductorwafer W at the time t4 is measured accurately with the radiationthermometer 120. The attained temperature T3 of the back surfacemeasured with the radiation thermometer 120 is transmitted to thecontroller 3. Based on the attained temperature T3 of the back surfaceof the semiconductor wafer W measured with the radiation thermometer120, the front surface temperature determining part 31 of the controller3 (FIG. 8) determines the processing temperature T2 that is atemperature attained by the front surface.

More specifically, the front surface temperature determining part 31first obtains an increased temperature ΔT by which the back surface ofthe semiconductor wafer W is increased in temperature from thepreheating temperature T1 by the irradiation with flashes. Specifically,the front surface temperature determining part 31 calculates theincreased temperature ΔT by subtracting the preheating temperature T1from the attained temperature T3 of the back surface.

The amount of heat transferred from the front surface to the backsurface of the semiconductor wafer W is defined according to themagnitude of energy applied to the front surface of the semiconductorwafer W by the irradiation with flashes from the flash lamps FL. Theincreased temperature ΔT of the back surface of the semiconductor waferW is defined by the amount of heat transferred from the front surface tothe back surface of the semiconductor wafer W. Specifically, theincreased temperature ΔT of the back surface of the semiconductor waferW during the irradiation with flashes is proportionate to the magnitudeof energy applied to the front surface of the semiconductor wafer W bythe irradiation with flashes. The specific heat of the siliconsemiconductor wafer W is known (substantially the same as the specificheat of silicon). Thus, as long as the magnitude of energy applied tothe front surface of the semiconductor wafer W can be obtained using theincreased temperature ΔT of the back surface of the semiconductor waferW, an increased temperature at the front surface of the semiconductorwafer W can be determined. By adding the determined increasedtemperature to the preheating temperature T1, the processing temperatureT2 as an attained temperature of the front surface can be determined.

Based on the aforementioned principle, the processing temperature T2 ofthe front surface of the semiconductor wafer W can be determined usingthe increased temperature ΔT of the back surface of the semiconductorwafer W. In this preferred embodiment, to determine the processingtemperature T2 more promptly, a correlation between the increasedtemperature ΔT and the processing temperature T2 as a front surfaceattained temperature is determined in advance. Based on thiscorrelation, the processing temperature T2 is determined.

FIG. 10 shows a correlation between the increased temperature ΔT of theback surface and an attained temperature of the front surface of thesemiconductor wafer W during the irradiation with flashes. As shown inFIG. 10, a linear relationship expressed by the following formula (1) isdefined between the increased temperature ΔT of the back surface and theprocessing temperature T2 as a front surface attained temperature of thesemiconductor wafer W during the irradiation with flashes:

T2=T1+aΔT  (1)

The correlation shown in FIG. 10 is determined in advance by experimentor simulation conducted using a dummy silicon wafer, for example. Thecorrelation shown in FIG. 10 is stored as a correlation table into themagnetic disk 35 of the controller 3 (see FIG. 8). Instead of thecorrelation table, the formula (1) may be stored into the magnetic disk35 of the controller 3.

Based on the correlation table shown in FIG. 10 or the correlationexpressed by the formula (1) between the increased temperature ΔT of theback surface and a front surface attained temperature of thesemiconductor wafer W, the front surface temperature determining part 31of the controller 3 determines a front surface attained temperature ofthe semiconductor wafer W during the irradiation with flashes using theincreased temperature ΔT. The controller 3 displays the determined frontsurface attained temperature of the semiconductor wafer W on the displaypart 33.

At time t5 when a predetermined period of time has elapsed after theflash heating process is finished, the halogen lamps HL are turned off.As a result, the temperature of the semiconductor wafer W drops rapidlyfrom the preheating temperature T1. The dropping temperature of thesemiconductor wafer W is measured with the contact thermometer 130 orthe radiation thermometer 120 and a result of the measurement istransmitted to the controller 3. The controller 3 checks the temperatureof the semiconductor wafer W using the measurement result to see whetherthis temperature has dropped to a predetermined temperature. After thetemperature of the semiconductor wafer W has dropped to thepredetermined temperature or less, the transfer arms 11 in a pair of thetransfer mechanism 10 again move horizontally from the retractedposition to the transfer operating position and move up. This makes thelift pins 12 project from the upper surface of the susceptor 74 toreceive the thermally processed semiconductor wafer W from the susceptor74. Next, the transport opening section 66 closed by the gate valve 185is opened and the semiconductor wafer W placed on the lift pins 12 istransported out of the apparatus by the transport robot outside theapparatus. In this way, the heating process on the semiconductor wafer Win the thermal processing apparatus 1 is completed.

In this preferred embodiment, from the stage of preheating by thehalogen lamps HL to the irradiation with flashes by the flash lamps FL,the radiation thermometer 120 is used for measuring the temperature of aback surface of a semiconductor wafer W to determine the increasedtemperature ΔT by which the back surface of the semiconductor wafer W isincreased in temperature from the preheating temperature T1 byirradiation with flashes. Based on the correlation between the increasedtemperature ΔT and a front surface attained temperature, the frontsurface temperature determining part 31 of the controller 3 determinesthe front surface attained temperature of the semiconductor wafer Wduring the irradiation with flashes using the increased temperature ΔT.Specifically, only the temperature of the back surface of thesemiconductor wafer W is measured with the radiation thermometer 120 andthe front surface attained temperature of the semiconductor wafer W isdetermined based on a result of this measurement.

A front surface of a semiconductor wafer W is provided with a pattern.Thus, the emissivity of the front surface is not known and is notuniform in the entire front surface. By contrast, a back surface of thesemiconductor wafer W is not provided with a pattern or a film depositedthereon to expose silicon. In other cases, a specific film is depositeduniformly on the back surface. Thus, the emissivity of the back surfaceis known. Hence, even with the noncontact radiation thermometer 120, thetemperature of the back surface of the semiconductor wafer W can stillbe measured accurately with favorable reproducibility. The increasedtemperature ΔT, by which the back surface of the semiconductor wafer Wis increased in temperature from the preheating temperature T1 byirradiation with flashes, is proportionate to the magnitude of energyapplied to the front surface of the semiconductor wafer W by theirradiation with flashes and does not depend on the detail of a patternformed on the front surface of the semiconductor wafer W (specifically,does not depend on the emissivity of the front surface). Thus, bymeasuring the temperature of the back surface of the semiconductor waferW with the radiation temperature 120 and obtaining the increasedtemperature ΔT from the preheating temperature T1 accurately, theprocessing temperature T2 as a front surface attained temperature of thesemiconductor wafer W during the irradiation with flashes can bedetermined.

A front surface attained temperature of a semiconductor wafer W can bedetermined only by providing the radiation thermometer 120 for receivingemitted light from a back surface of the semiconductor wafer W andmeasuring a temperature without requiring provision of a sensor formeasuring the intensity of emitted light from a front surface of thesemiconductor wafer W. Specifically, according to the present invention,the temperature of the front surface of the semiconductor wafer W can bemeasured with a simple structure irrespective of the condition of thefront surface of the semiconductor wafer W.

In addition to the preferred embodiment of the present inventiondescribed above, the present invention can be changed in various wayswithout departing from the scope of the invention. For example, in theaforementioned preferred embodiment, a semiconductor wafer W to beprocessed is made only of silicon (while impurities of a tiny quantityare added to the wafer W, effect on the specific heat of thesemiconductor wafer W caused by this quantity is ignorable). However,such a semiconductor wafer W is not the only processing target. Even asemiconductor substrate having a stack of layers made of differentmaterials can still be subjected to temperature measurement using thetechnique of the present invention. For example, by employing the samemethod as that of the aforementioned preferred embodiment, thetemperature of a back surface of a semiconductor substrate containinggermanium (Ge) epitaxially grown on a silicon base can be measured withthe radiation thermometer 120 to obtain the increased temperature ΔTduring irradiation with flashes. Then, a front surface attainedtemperature of this substrate can be determined using the increasedtemperature ΔT. In the substrate including the germanium epitaxial filmformed on a front surface, the emissivity of the back surface of thissubstrate is known as silicon is exposed at the back surface. Thus, evenin this substrate, the temperature of the back surface can still bemeasured accurately with the radiation thermometer 120.

In the case of a substrate including a silicon base and a film formed onthe silicon base and made of a material different from silicon, thespecific heat of a front surface and its vicinity of the substratediffers from that of a substrate made only of silicon. To measure thetemperature of such a substrate including a stacked layer made of amaterial different from silicon, the temperature correcting part 32 ofthe controller 3 (FIG. 8) corrects a front surface attained temperature(a temperature determined based on the specific heat of silicon)determined by the front surface temperature determining part 31. Thetemperature correcting part 32 makes this correction based on thespecific heats of the materials forming the substrate. In the case ofthe aforementioned substrate including the silicon base and thegermanium epitaxial film formed on the silicon base, for example, thetemperature correcting part 32 reduces a front surface attainedtemperature determined by the front surface temperature determining part31 by about three percent based on a difference in specific heat betweensilicon and germanium. In this way, a front surface attained temperatureof this substrate can be determined.

The emissivity of a front surface is very difficult to measure in asubstrate having a stack structure such as a substrate including asilicon base and a germanium epitaxial film formed on the silicon base.However, by employing the aforementioned technique, an attainedtemperature of the front surface of the substrate can be measuredeasily. Specifically, the technique according to the present inventionis used appropriately particularly for measuring a front surfaceattained temperature of a substrate having such a stack structure andwhere the emissivity of a front surface is difficult to measure.

In the aforementioned preferred embodiment, a front surface attainedtemperature of a semiconductor wafer W during irradiation with flashesis determined using the increased temperature ΔT of a back surface ofthe semiconductor wafer W. Alternatively, a front surface attainedtemperature of a semiconductor wafer W may be determined using anintegral of the increased temperature ΔT. More specifically, the frontsurface temperature determining part 31 determines a front surfaceattained temperature of a semiconductor wafer W using an integralobtained by integrating the increased temperature ΔT with respect totime by which a back surface of the semiconductor wafer W is increasedin temperature from the preheating temperature T1 during irradiationwith flashes (specifically, this integral is shown as a dashed region ofFIG. 9).

As a result of irradiation with flashes in an extremely short period oftime, a period of time when the temperature of a back surface of asemiconductor wafer W increases from the preheating temperature T1 isalso extremely short. Meanwhile, time of sampling with the radiationthermometer 120 can be reduced only to limited time. This may make itimpossible to measure the temperature T3 attained by the back surface ofthe semiconductor wafer W with the radiation thermometer 120 to coincidewith the time t4 of FIG. 9. This causes the risk of an error in theincreased temperature ΔT of the back surface of the semiconductor waferW during irradiation with flashes. By determining a front surfaceattained temperature of the semiconductor wafer W using an integral ofthe increased temperature ΔT, a measurement error of the increasedtemperature ΔT to be caused by sampling time with the radiationthermometer 120 is reduced. This can enhance accuracy in determining afront surface attained temperature of the semiconductor wafer W.

In the aforementioned preferred embodiment, 30 flash lamps FL areprovided in the flash heating unit 5. However, the number of the flashlamps FL is not limited to 30 but it can be determined arbitrarily.Further, the flash lamps FL are not limited to xenon flash lamps butthey may also be krypton flash lamps. Additionally, the number of thehalogen lamps HL in the halogen heating unit 4 is not limited to 40 butit can be determined arbitrarily.

In the aforementioned preferred embodiment, a semiconductor wafer W ispreheated by being irradiated with halogen light from the halogen lampsHL. However, this is not the only method of the preheating. Thesemiconductor wafer W may be preheated by being placed on a hot plate.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It istherefore understood that numerous modifications and variations can bedevised without departing from the scope of the invention.

What is claimed is:
 1. A thermal processing method for heating asubstrate by irradiating said substrate with a flash, comprising thesteps of: (a) preheating said substrate by increasing said substrate intemperature to a predetermined preheating temperature before irradiatingsaid substrate with a flash; (b) heating said substrate increased intemperature to said preheating temperature by irradiating a frontsurface of said substrate with a flash; (c) measuring a differencetemperature between a back surface attained temperature attained by aback surface of said substrate from said preheating temperature byirradiation with a flash and said preheating temperature; and (d)determining a front surface attained temperature of said substrateduring irradiation with a flash based on said difference temperature.